Q43000: Passing Two-Dimensional Arrays between C and FORTRAN

Article: Q43000
Product(s): See article
Version(s): 5.10   | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | H_FORTRAN | mspl13_c
Last Modified: 18-MAY-1989

When passing two-dimensional arrays from FORTRAN to C and vice versa,
it is important to note that the indexing conventions for the two
languages are different.

C arrays are indexed row followed by column; or, the second index
varies the quickest. However, FORTRAN is indexed just the opposite: in
FORTRAN, two-dimensional arrays are indexed with the first indice
varying the quickest. Thus, passing two-dimensioned arrays requires
modification to either the C code or the FORTRAN code.

For more information regarding passing arrays between C and FORTRAN,
please see Page 127, Section 9.1.2, "Array Declaration and Indexing,"
in the "Microsoft Mixed-Language Programming Guide for the MS-DOS
Operating System."

The following code samples define an array in a common block in
FORTRAN, then use C to print the arrays to the screen:

c     program mix_for.for
c
c
c     this is to be used with mix_c.c......
c
      subroutine test ()
      common/cblock/array(0:8,0:1)
      integer*4 i,j

      do 20 i = 0,8,1
        do 30 j = 0,1,1
        array(i,j) = i
      write(6,*)'the value of (',i,':',j,') is ',array(i,j)
  30  continue
  20  continue
      end

/*  program mix_c.c

    this program is to be used with  mix_for.for......
    */

#include <stdio.h>

struct common_blk{
                 float array[2][9]; /* note that the subscripts
                                        of the array are inverted */
                 };

extern void fortran test (void);

extern struct common_blk fortran cblock;

main()
{
    int i,j;
    test();
    for(i=0;i<=8;i++)
        for(j=0;j<=1;j++)
            printf("\nthe value of %d:%d is %f"
                          ,i,j,cblock.array[j][i]);
}

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